So do people think it's worth the risk of setting power to idle without knowing for certain if a reverser is the cause?
Risk ??? of what?
In an actual event, the crew reported flickering unlock lights during initial climb. They discussed the possibility of false warnings (loose connections, wiring etc.) but decided it would be prudent to follow the FCOM and pull the affected engine back to idle. The unlock light ceased so they once again advanced the throttle to maintain climb profile. The reverser then deployed and rolled the aircraft over to 180 deg in a matter of seconds. The airforced trained PF then completed the roll through 360 deg and requested clearance to return to the field.
On ground examination found nothing wrong.